Spark plug



- Patented Jan. 20, 1942' SPARK PLUG Edward B. Nowosielski, Bloomfield, N. .L, assignor to Edison- Splitdorf Corporation, West Orange, N. J a corporation of New Jersey Application July 18, 1940, Serial No. 346,115

' Claims.

This invention relates to the construction of a spark plug of what may be termed a diminutive size, especially adapted for use on aeroplane engines where space, size and weight are important factors,

Aeroplane engines today are obliged to operate at approximately full load for relatively long periods of time, and as most of these engines, as now built, are of a much greater horsepower than an automobile or truck engine, the conditions imposed on the spark plugs are much more severe than in an automobile or truck.

So far as I am at present aware, no one heretofore has been able to make, for an aircraft engine, a spark plug of a ten-millimeter size, this dimension being the diameter of the threaded end of the plug which is screwed into the engine cylinder. One of the difficulties of constructing such a small plug, using a ceramic insulator for the central electrode, is that by just screwing the plug into the engine the insulator is apt to be crushed or broken due to the thin wall of th shell carrying the insulator.

It is therefore the principal object of my invention to provide a spark plug of relatively small dimensions, but one which will meet the requirement necessary in an aeroplane engine.

While producing a spark plug which will meet the exact service heretofore referred to, I have accomplished this in a relatively inexpensive manner.

My improved type of construction is set forth in the annexed drawing, wherein Figure 1 is a sectional view, on a scale between three and four times the size of the article itself, through a plug of ten-millimeter size, the ignition cable being shown in disconnected position from the central electrode.

Figure 2 is an end view of the firing end of the plug.

Figure 3 is a composite view, the side to the left of the center line being of a fourteen-millimeter size, while the'part to the right of the center line illustrates the same type of plug made in eighteen-millimeter size, the scale being the same as in Figure 1.

Figure 4 is an end view of Figure 3.

In the different views, I is a shell having an externally threaded end 2 which is adapted to be screwed into an engine cylinder. The firing end of the plug is preferably provided with a plurality of ground electrodes 3 which, as shown in Figure 1, are inserted into holes formed at an angle in the end of the shell. These holes extend through the outer wall of the shell and after the electrodes 3 have been put in place, they are preferably brazed in position, and then the thread 2 is formed, so that the outer ends of the ground electrodes 3 form a part of the thread. This provides a direct contact between the ground electrodes 3 and the cylinder wall, so that the heat from these electrodes is transmitted not only to the shell of the plug, but directly to the wall of the engine, thereby aiding in the cooling of the electrodes which are arranged around the central electrode 4 as indicated in Figure 2.

The central electrode 4 has applied to its entire surface-except the terminal end which 'is positioned within a recess 'l-before it is inserted into the ceramic insulator 5, a suitable enamel paste-type cement 6. Mounted on the external surface of the insulator 5 is a metallic sleeve 8 having a flange 9 which is adapted to engage a seat In on the outer end of the shell I. Before mounting the sleeve 8 on the insulator, the outer surface of the insulator, which is to be engaged by the sleeve, and the internal surface of the sleeve are treated or have applied thereto a similar cement H as is used to cement the central electrode 4 to the insulator 5. The sleeve 8 is made of a material which has the same coefficient of expansion as the cement 6 and insulator v5 so as to prevent any breaking away of the may be applied. Preferably, a copper gasket ll is used at the seat' In so that the flange 9 will be pressed against this gasket by the threaded end l5 of an elongated gland Hi. The threaded end 15 is adapted to engage threads on the outer end I! of the shell I which is preferably provided with a hex format'on 18 to receive a wrench. Likewise, the gland I6 is provided with a, hex

formation I9 for screwing the gland into the end ll of the shell I.

The inner end 28 of the gland I8 is formed to provide considerable area for engagement with the flange 9 of the sleeve 8; also, to provide'an internal seat for a flangedcollar' 2| wh'ch is used for the purpose of positioning a pair of concentrically arranged tubular members 22 and 23, the

tubular member22 being of suitable insulating material, preferably of mica wrapped in tubular form, .fltting snugly within the metal tube 23 which, in turn, fits snugly within the clamping end of the gland l8. As will be seen from Figure 1, both the tubular members extend a considerable distance over the insulator 5, and a space 24 is provided between the metal tube 23 and the wall of the gland l8 for a considerable part of its length.

The outer ends of the tubular members 22 and 23 are supported by a flanged collar 25 similar to 2|, the flange of the collar being held between washers 28 and 21. The washer 28 is positioned against a shoulder 28 on the gland "5, while the washer 2'! is held in position by spinning over the gland at 29.

The outer end of the electrode 4 terminates in a ball-type formation 30, over which is adapted to be pressed a terminal 3| formed circular in shape and having splits 32 to give a spring eiiect when pushed over the ball 38. The terminal 3| is fastened to the conductor of an ignition cable 33 which preferably makes a close sliding fit with the tubular insulator 22, so that when the cable is pushed into position, whereby the terminal 3| will engage the ball 38, all of the metal parts of the'live end of the plug are deeply and thoroughly concealed within the gland I8, so that there is no possibility of moisture interfering with the action of the plug, and the insulator 22 prevents any deleterious leakage from the electrode 4 to the wall of the gland Hi. If desired, a gasket-type washer 34 may be used between the clamping end of the gland l6 and the flange 9 which supports the insulator 5.

With this construction, it will be seen that in the assembly of the plug, on screwing the gland l8 into the end ll of the shell I, the pressure is applied to the flange 9 and not to the insulator as in the ordinary type of construction, and hence the insulator is not put under any strain due to the assembly operation. It may be noted that the end 35 of the central electrode 4 may be made of platinum, but welded at 36 to the electrode 4 which is made of much cheaper material.

While the electrodes themselves are relatively small and may heat up faster, on the other hand, they are cooled much quicker when a fresh charge of air and fuel is taken into the cylinder, so that there is no danger of pre-flring and the metal sleeve 8 around the insulator 5 acts to convey heat outwardly to the shell and the gland l8.

In the fourteen-millimeter construction shown in the left-half of Figure 3, the general construction is the same as in Figure 1, except that the sleeve 8 has a somewhat difierently formed flange 9, this being indicated as on a bevel. Likewise, the inner end of the gland I5 is beveled to engage a gasket 34; also, the shell I is bored out somewhat larger 'at the place where the sleeve 8 is positioned so as to provide a thicker wall for the sleeve. In addition, the ground electrodes 3 are first installed in a washer or disc 31 which is held in position in the end of the shell I by spinning the same over at 38. In this form, the ends of the electrodes 3 are bent inwardly a distance at 39 to provide a reater firing area. Also, in Figure 3, the ball 30 is positioned within the recess 1 instead of projecting slightly without it as in Figure 1.

In the right half of Figure 3, the eighteenmilliineter construction is the same as in the left half, except that the sleeve 8 is placed in reverse position, thereby bringing the clamping pressure of the gland l8 farther down in the shell.

While .I prefer to use the metal tube 23 in conjunction with the tubular member 22 which is of suitable insulating material, the metal tube may be dispensed with by making the insulating tube thicker, or not boring the inner end of the gland I8 quite so large as it is when the metal tube is used in conjunction with the insulating tube.

What I claim is:

1. A spark plug including a shell externally threaded at one end for screwing into an engine cylinder and internally threaded at its opposite end to receive a gland, and further having an annular seat adjacent the inner end of said internal threads, a ceramic insulator, a central electrode cemented longitudinally of its length within the insulator and having its cable end terminating near the end of the insulator, a sleeve cemented to the exterior surface of said insulator, the sleeve having a flange to engage said seat in the shell, an elongated gland threaded at one end to engage the internally threaded end of the shell, this end of the gland acting to apply pressure to the flange of said sleeve, a tubular insulator and a metallic tube positioned, the first-mentioned within the second, and both carried within the gland and for substantially its full length and encompassing the central electrode insulator for a consider: able distance, and ground electrodes carried by 1thedshell in operative relation to the central elecro e.

2. A spark plug including a shell externally threaded at one end for screwing into an engine cylinder and internally threaded at its opposite end to receive a gland, and further having an annular seat adjacent the inner end of said internal threads, a ceramic insulator, a central electrode cemented longitudinally of its length within the insulator and having its cable end terminating near the end of the insulator, a sleeve cemented to the exterior surface of said insulator, the sleeve having a flange to engage said seat in the shell, an elongated gland threaded at one end to engage the internally threaded end of the shell, this end of the gland having an end surface of considerable area, a gasket between this end surface and the flange on said sleeve, 9. flanged collar within the gland and positioned against the inner part of said end surface, a pair of I concentrically arranged tubular members carried within the gland and having their inner ends located by said collar, the inner tubular member being of suitable insulation, while the outer tubular member is of metal and spaced a distance from the inner wall of the gland for a considerable of its length, means for supporting the two tubular members at the outer end of said gland and at least one ground electrode carried by the free end of the shell in operative relation to the central electrode.

3. A spark plug including a shell externally threaded at one end for screwing into an engine cylinder and internally threaded at its opposite end to receive a gland, and further having an annular seat adjacent the inner end of said internal threads, a ceramic insulator, a central electrode cemented longitudinally of its length within the insulator and having its cable end terminating near the end of the insulator, a sleeve cemented to .the exterior surface of said insulator, the sleeve having a flange to engage said seat in the shell, an elongated gland threaded at one end to engage the internally threaded end of the shell, this end of the gland having an end surface of considerable area to apply pressure to the flange of said sleeve, 9. pair of concentrically arranged tubular members supported within and at opposite ends of the gland, the inner tubular member being of suitable insulating material, the electrode insulator projecting into the inner end of the tubular insulator and at least one ground electrode attached to the free end of the said shell in cooperative relation to the central electrode.

4. A spark plug including a shell externally threaded at one end for screwing into an engine cylinder and internally threaded at its opposite end to receive a gland, and further having an annular seat adjacent the inner end of said internal threads, a ceramic insulator, a central electrode cemented longitudinally of its length within the insulator and having its cable end, terminating near the end of the insulator, a sleeve cemented to the exterior surface of said insulator, the sleeve having a flange to engage said seat in the shell, an elongated gland having two bores of different diameter and being threaded at least at the end having the smaller bore so as to fit the internally threaded end of the shell, this end also havin a formation to apply pressure direct or through a gasket to the flange of said sleeve, a pair of concentrically arranged tubular members, the inner one being of insulating material and both extending with a snug fit into the smaller bore of the gland and supported therein, means at the free end of the gland for supporting the outer end of the tubular members, the

central electrode insulator extending into the tubular member for only a part of its length, and at least one ground electrode carried by the shell at its free end.

5. A spark plug including a shell and an elongated gland determining the length of the cable end of the plug, the shell being threaded at one end for attachment to an engine cylinder and threaded at the opposite end to receive the gland, a seat within the gland end of theshell, an insulator and an electrode carried thereby and cemented thereto, a flanged metallic sleeve cemented to the outer wall ofsaid insulator, the flange engaging said seat and held thereto by the inner end of said gland, at least one tubular member of suitable insulating material, such as mica, carried within the gland and surrounding the cable end of the electrode insulator and extending substantially the length 01 the elongated gland, means for supporting the tubular member at the free end of the gland, and at least one ground electrode carried by the shell.

6. A spark plug as defined in claim 5, further defined in that a plurality of ground electrodes are used and they extend at an angle through the end or the shell and some parts of the threads at this end of the shell are out directly into the electrodes.

7. A spark plug as defined in claim 5, furtherlating material is spaced from the wallet the gland for a greater part of its length and has a diameter so a standard ignition cable fits its inner wall very snugly, whereby when the cable is pushed therein so its terminal engages the end of thercentral electrode, all the bare parts in the ignition circuit are concealed well within the land.

9. A spark plug as set forth inclaim 5, further defined in that a metallic tubular member, similar to the one of insulating material, is positioned thereover and extends to the cable-entering end of the plug.

10. A spark plug including a shell externally threaded at one end for screwing into an, engine cylinder and internally threaded at its opposite end to receive a gland, and further having an annular seat adjacent the inner end of said internal threads, a single-piece ceramic insulator, a central electrode cemented longitudinally of its length within the insulator and having its cable end terminating near the end or the insulator, a sleeve cemented to the exterior surface of said insulator, the sleeve having a flange to engage said seat in the a shell, an elongated gland threaded at one end to engage the internally threaded end of the shell, this end of the gland acting to apply pressure to the flange of said sleeve,- at least one tubular member and of insulating material carried within the gland and for the greater part of its length and encompassing the central electrode and its insulator for a distance' at its cable end, and at least one ground electrode carried by the shell in operative relation to the central electrode.

EDWARD B. N OWOSIELSKI. 

